SQL * Insert(CATEGORIES)
           (CAT_ID, some_value);

SQL * Update(CATEGORIES)(CAT_ID, update_value).Where(ID == key);

Sql sql;
sql * Select(ID, CAT_ID).From(CATEGORIES).Where(... some condition ...);

now the loop can look like

int id, cat_id;
while(sql.Fetch(id, cat_id)) ...

or

while(sql.Fetch()) { .. sql[ID] .. sql[0] .. }

(you can use either ids or indexes).

Alternatively, you can use S_CATEGORIES structure to work with the whole record.